In countries where pertussis is no longer a public health problem, bivalent vaccine in its pediatric form (DT) may be used for booster doses in preschool children. The adult form (Td) should be used for booster doses in children aged seven years and over and in adolescents and adults. The following 3 DTP immunization schedules are in widespread use: a) 3 doses: 3 primary doses of DTP vaccine given during the 1st year of life, b) 4 doses: primary series of 3 doses reinforced with a booster dose usually administered around the 2nd or 3rd year of life and c) 5 doses: primary series of 3 doses reinforced with a 1st booster dose in the 2nd year of life and a 2nd booster given before entering school at the age of 4-6 years. Diphtheria toxoid is also included in the pentavalent DTP–HBV–Hib vaccine. Booster doses: A regime of routine booster doses approximately every 10 years is indicated for the maintenance of immunity.